MailTime
Micro-service package for mail queue, with Server and Client API.
Build on top of nodemailer
package.
Every MailTime
instance can be configured to be a Server or Client.
Main difference of Server from Client - Server handles queue and actually sends email.
While Client is only put emails into the queue.
ToC
Main features:
- 👨🔬 ~92% tests coverage;
- 📦 Two simple dependencies, written from scratch for top performance;
- 🏢 Synchronize email queue across multiple servers;
- 💪 Bulletproof design, built-in retries.
How does it work?
Redundant solution for email transmission.
Single point of failure
Issue - classic solution with the single point of failure:
|----------------| |------| |------------------|
| Other mailer | ------> | SMTP | ------> | ^_^ Happy user |
|----------------| |------| |------------------|
The scheme above will work as long as SMTP service is available
or connection between your server and SMPT is up. Once network
failure occurs or SMTP service is down - users won't be happy
|----------------| \ / |------| |------------------|
| Other mailer | --X---> | SMTP | ------> | 0_o Disappointed |
|----------------| / \ |------| |------------------|
^- email lost in vain
Single SMTP solution may work in case of network or other failures
As long as MailTime has not received confirmation what email is sent
it will keep the letter in the queue and retry to send it again
|----------------| / |------| |------------------|
| Mail Time | --X---> | SMTP | ------> | ^_^ Happy user |
|---^------------| / |------| |------^-----------|
\-------------/ ^- We will try later /
\- put it back into queue /
\----------Once connection is back ------/
Multiple SMTP providers
Backup scheme with multiple SMTP providers
|--------|
/--X--| SMTP 1 |
/ ^ |--------|
/ \--- Retry with next provider
|----------------|/ |--------| |------------------|
| Mail Time | ---X--> | SMTP 2 | /->| ^_^ Happy user |
|----------------|\ ^ |--------| / |------------------|
\ \--- Retry /
\ |--------| /
\---->| SMTP 3 |--/
|--------|
Cluster issue
Let's say you have an app which is growing fast. At some point, you've decided to create a "Cluster" of servers to balance the load and add durability layer.
Also, your application has scheduled emails, for example, once a day with recent news. While you have had single server emails was sent by some daily interval. So, after you made a "Cluster" of servers - each server has its own timer and going to send a daily email to our user. In such case - users will receive 3 emails, sounds not okay.
Here is how we solve this issue:
|===================THE=CLUSTER===================| |=QUEUE=| |===Mail=Time===|
| |----------| |----------| |----------| | | | |=Micro-service=| |--------|
| | App | | App | | App | | | | | |-->| SMTP 1 |------\
| | Server 1 | | Server 2 | | Server 3 | | | <-------- | |--------| \
| |-----\----| |----\-----| |----\-----| | | --------> | |-------------|
| \---------------\----------------\----------> | | | |--------| | ^_^ |
| Each of the "App Server" or "Cluster Node" | | | | |-->| SMTP 2 |-->| Happy users |
| runs Mail Time as a Client which only puts | | | | | |--------| |-------------|
| emails into the queue. Aside to "App Servers" | | | | | /
| We suggest running Mail Time as a Micro-service | | | | | |--------| /
| which will be responsible for making sure queue | | | | |-->| SMTP 3 |-----/
| has no duplicates and to actually send emails | | | | | |--------|
|=================================================| |=======| |===============|
Features
- Queue - Managed via MongoDB, and will survive server reboots and failures
- Support for multiple server setups - "Cluster", Phusion Passenger instances, Load Balanced solutions, etc.
- Emails concatenation by addressee email - Reduce amount of sent emails to a single user with concatenation, and avoid mistakenly doubled emails
- When concatenation is enabled - Same emails won't be sent twice, if for any reason, due to bad logic or application failure emails are sent twice or more times - this is solution to solve this annoying behavior
- Balancing for multiple nodemailer's transports, two modes -
backup
and balancing
. Most useful feature - allows to reduce the cost of SMTP services and add durability. So, if any of used transports are failing to send an email it will switch to next one - Sending retries for network and other failures
- Template support with Mustache-like placeholders
Installation
If you're working on Server functionality - first you will need nodemailer
, although this package is meant to be used with nodemailer
, it's not added as the dependency, as it not needed by Client, and you're free to choose nodemailer
's version to fit your needs:
npm install --save nodemailer
Install MailTime package:
# for node@>=8.9.0
npm install --save mail-time
# for node@<8.9.0
npm install --save mail-time@=0.1.7
Basic usage
Require package:
const MailTime = require('mail-time');
Create nodemailer's transports (see nodemailer docs):
const transports = [];
const nodemailer = require('nodemailer');
const directTransport = require('nodemailer-direct-transport');
const directTransportOpts = {
pool: false,
direct: true,
name: 'mail.example.com',
from: 'no-reply@example.com',
};
transports.push(nodemailer.createTransport(directTransport(directTransportOpts)));
transports[0].options = directTransportOpts;
transports.push(nodemailer.createTransport({
host: 'smtp.example.com',
from: 'no-reply@example.com',
auth: {
user: 'no-reply',
pass: 'xxx'
},
}));
transports.push(nodemailer.createTransport({
host: 'smtp.gmail.com',
from: 'no-reply@mail.example.com',
auth: {
user: 'no-reply@mail.example.com',
pass: 'xxx'
},
}));
transports.push(nodemailer.createTransport({
host: 'smtp.sparkpostmail.com',
port: 587,
from: 'no-reply@mail2.example.com',
auth: {
user: 'SMTP_Injection',
pass: 'xxx'
},
}));
Create mail-time
Server, it is able to send and add emails to the queue.
We will need connect to MongoDB first:
const MongoClient = require('mongodb').MongoClient;
const MailTime = require('mail-time');
const dbName = 'DatabaseName';
MongoClient.connect(process.env.MONGO_URL, (error, client) => {
const db = client.db(dbName);
const mailQueue = new MailTime({
db,
type: 'server',
strategy: 'balancer',
transports,
from(transport) {
return '"Awesome App" <' + transport.options.from + '>';
},
concatEmails: true,
concatDelimiter: '<h1>{{{subject}}}</h1>',
template: MailTime.Template
});
});
Create the Client to add emails to queue from other application units, like UI unit:
const MongoClient = require('mongodb').MongoClient;
const MailTime = require('mail-time');
const dbName = 'DatabaseName';
MongoClient.connect(process.env.MONGO_URL, (error, client) => {
const db = client.db(dbName);
const mailQueue = new MailTime({
db,
type: 'client',
strategy: 'balancer',
concatEmails: true
});
});
Send email:
mailQueue.sendMail({
to: 'user@gmail.com',
subject: 'You\'ve got an email!',
text: 'Plain text message',
html: '<h1>HTML</h1><p>Styled message</p>'
});
Meteor.js usage:
Meteor.js Installation:
Installation & Import (via NPM):
Install NPM MailTime package:
meteor npm install --save mail-time
ES6 Import:
import MailTime from 'mail-time';
Installation & Import (via Atmosphere):
Install Atmosphere ostrio:mailer package:
meteor add ostrio:mailer
ES6 Import:
import MailTime from 'meteor/ostrio:mailer';
Usage:
import { MongoInternals } from 'meteor/mongo';
import MailTime from 'mail-time';
import nodemailer from 'nodemailer';
import directTransport from 'nodemailer-direct-transport';
const transports = [];
const directTransportOpts = {
pool: false,
direct: true,
name: 'mail.example.com',
from: 'no-reply@example.com',
};
transports.push(nodemailer.createTransport(directTransport(directTransportOpts)));
transports[0].options = directTransportOpts;
const mailQueue = new MailTime({
db: MongoInternals.defaultRemoteCollectionDriver().mongo.db,
transports,
from(transport) {
return '"Awesome App" <' + transport.options.from + '>';
}
});
API
new MailTime(opts)
constructor
opts
{Object} - Configuration objectopts.db
{Db} - [Required] Mongo's Db
instance. For example returned in callback of MongoClient.connect()
opts.type
{String} - [Optional] client
or server
, default - server
opts.from
{Function} - [Optional] A function which returns String of from
field, format: "MyApp" <user@example.com>
opts.transports
{Array} - [Optional] An array of nodemailer
's transports, returned from nodemailer.createTransport({})
opts.strategy
{String} - [Optional] backup
or balancer
, default - backup
. If set to backup
, first transport will be used unless failed to send failsToNext
times. If set to balancer
- transports will be used equally in round robin chainopts.failsToNext
{Number} - [Optional] After how many failed "send attempts" switch to next transport, applied only for backup
strategy, default - 4
opts.prefix
{String} - [Optional] Use unique prefixes to create multiple MailTime
instances on same MongoDBopts.maxTries
{Number} - [Optional] How many times resend failed emails, default - 60
opts.interval
{Number} - [Optional] Interval in seconds between send re-tries, default - 60
opts.zombieTime
{Number} - [Optional] Time in milliseconds, after this period - pending email will be interpreted as "zombie". This parameter allows to rescue pending email from "zombie mode" in case when: server was rebooted, exception during runtime was thrown, or caused by bad logic, default - 32786
. This option is used by package itself and passed directly to JoSk
packageopts.keepHistory
{Boolean} - [Optional] By default sent emails not stored in the database. Set { keepHistory: true }
to keep queue task as it is in the database, default - false
opts.concatEmails
{Boolean} - [Optional] Concatenate email by to
field, default - false
opts.concatSubject
{String} - [Optional] Email subject used in concatenated email, default - Multiple notifications
opts.concatDelimiter
{String} - [Optional] HTML or plain string delimiter used between concatenated email, default - <hr>
opts.concatThrottling
{Number} - [Optional] Time in seconds while emails are waiting to be concatenated, default - 60
opts.revolvingInterval
{Number} - [Optional] Interval in milliseconds in between queue checks, default - 256
. Recommended value — between opts.minRevolvingDelay
and opts.maxRevolvingDelay
opts.minRevolvingDelay
{Number} - [Optional] Minimum revolving delay — the minimum delay between tasks executions in milliseconds, default - 64
. This option is passed directly to JoSk
packageopts.maxRevolvingDelay
{Number} - [Optional] Maximum revolving delay — the maximum delay between tasks executions in milliseconds, default - 256
. This option is passed directly to JoSk
packageopts.template
{String} - [Optional] Mustache-like template, default - {{{html}}}
, all options passed to sendMail
is available in Template, like to
, subject
, text
, html
or any other custom option. Use {{opt}}
for string placeholders and {{{opt}}}
for html placeholders
sendMail(opts [, callback])
- Alias -
send()
opts
{Object} - Configuration objectopts.sendAt
{Date} - When email should be sent, default - new Date()
use with caution on multi-server setup at different location with the different time-zonesopts.template
- Email specific template, this will override default template passed to MailTime
constructoropts.concatSubject
- Email specific concatenation subject, this will override default concatenation subject passed to MailTime
constructoropts[key]
{Mix} - Other custom and NodeMailer specific options, like text
, html
and to
, see more here. Note attachments
should work only via path
, and file must exists on all micro-services serverscallback
{Function} - Callback called after the email was sent or failed to be sent. Do not use on multi-server setup
static MailTime.Template
Simple and bulletproof HTML template, see its source. Usage:
const MailTime = require('mail-time');
const mailQueue = new MailTime({
db: db,
template: MailTime.Template
});
mailQueue.sendMail({
to: 'user@gmail.com',
template: MailTime.Template
});
Template Example
mailQueue.sendMail({
to: 'user@gmail.com',
userName: 'Mike',
subject: 'Sign up confirmation',
text: 'Hello {{userName}}, \r\n Thank you for registration \r\n Your login: {{to}}',
html: '<div style="text-align: center"><h1>Hello {{userName}}</h1><p><ul><li>Thank you for registration</li><li>Your login: {{to}}</li></ul></p></div>',
template: '<body>{{{html}}}</body>'
});
Testing
- Clone this package
- In Terminal (Console) go to directory where package is cloned
- Then run:
Test NPM package:
# Before run tests make sure NODE_ENV === development
# Install NPM dependencies
npm install --save-dev
# Before run tests you need to have running MongoDB
DEBUG="true" EMAIL_DOMAIN="example.com" MONGO_URL="mongodb://127.0.0.1:27017/npm-mail-time-test-001" npm test
# Be patient, tests are taking around 2 mins
Test Atmosphere (meteor.js) package:
# Default
EMAIL_DOMAIN="example.com" meteor test-packages ./ --driver-package=meteortesting:mocha
# With custom port
DEBUG="true" EMAIL_DOMAIN="example.com" meteor test-packages ./ --driver-package=meteortesting:mocha --port 8888
# With local MongoDB and custom port
DEBUG="true" EMAIL_DOMAIN="example.com" MONGO_URL="mongodb://127.0.0.1:27017/meteor-mail-time-test-001" meteor test-packages ./ --driver-package=meteortesting:mocha --port 8888
# Be patient, tests are taking around 2 mins
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